1. Technical Field
The present invention relates to an audio decoding device, an audio decoding method, a program, and an integrated circuit, and in particular, to an audio decoding device that decodes a plurality of frame data obtained by coding time signals being respectively divided into frame sections each including an overlapping section.
2. Background Art
In recent years, multi-channel audio reproducing apparatuses have been upgraded, and the need for multi-channels is increasing. Thus, the MPEG Surround that is a coding technique of multi-channel signals has been standardized according to the Moving Picture Experts Group (MPEG). According to the MPEG Surround, multi-channel signals are coded into monophonic or stereo signals while maintaining a realistic sound experience obtained by the multi-channel signals. The monophonic or stereo signals are broadcasted or distributed to reproducing apparatuses each including an audio decoding device, via conventional broadcasting or distribution. Such audio decoding devices decode the monophonic or stereo signals into the multi-channel signals (for example, see Non-patent Reference 1).
The MPEG Surround uses bit rates lower than those of the DTS (Digital Theater Systems) and the Dolby Digital, or Audio Code number 3 (AC3) that is a conventional coding technique of multi-channel signals, and maintains compatibility with other conventional coding techniques, such as the conventional AAC (Advanced Audio Coding) and AAC+SBR (Spectral Band Replication). Thus, the MPEG Surround should be used for mobile broadcasting, such as digital radio and one-segment broadcasting.
Here, a general audio decoding device will be described with reference to FIG. 1.
A conventional audio decoding device 10 in FIG. 1 generates an output waveform 106 by decoding a stream 100.
The stream 100 is a bit stream obtained by coding audio signals using an audio coding device, and is generally made up of access units. The access units of the stream 100 are referred to as frames hereinafter. Furthermore, each of the coded audio signals included in the frames is referred to as frame data. The frame data is data obtained by coding original audio (audio signals before coding) for each predetermined section. Here, the predetermined sections are referred to as frame sections.
The audio decoding device 10 includes a decoding unit 101, an orthogonal transformation unit 103, and an output unit 105.
The decoding unit 101 is an audio decoder that analyzes a structure of the stream 100, decodes the coded stream 100 using a Huffman code, and inversely quantizes the decoded stream 100 for each frame to generate spectrum coefficients 102.
The orthogonal transformation unit 103 transforms the spectrum coefficients 102 to time signals 104 based on a conversion algorithm defined by the decoding unit 101.
The output unit 105 generates the output waveform 106 from the time signals 104.
Furthermore, when the decoding unit 101 detects occurrence of an error, the conventional audio decoding device 10 performs mute processing that clears a corresponding one of the time signals 104 in a frame where the error occurs (hereinafter referred to as error frame) by 0, or performs repeat processing that repeatedly uses the past time signals 104.
Furthermore, what is also known is an audio decoding device that performs interpolation that maintains continuity by interpolating a time signal in a frame section where the error occurs (hereinafter referred to as error frame section), between time signals that are present prior to and subsequent to the error frame section (for example, see Patent Reference 1).    Non-Patent Reference 1: 118th AES convention, Barcelona, Spain, 2005, Convention Paper 6447    Patent Reference 1: Japanese Unexamined Patent Application Publication No. 2002-41088